This invention relates to methods for removing hydrophobic deposits from a substrate.
In painting processes, especially those using spray application techniques, large quantities of paint are often deposited on the walls and floors in the painting area. Upon accumulation, these deposits tend to block floor grates and exhaust stacks thereby creating a safety hazard. Thus, the floor grates and exhaust stacks must be cleaned frequently and at regular intervals.
Conventionally, cleaning of such paint deposits has been performed by various mechanical separation means such as peeling, scraping, brushing or melting the paint from the substrate or by chemical means such as alkali or solvent cleaning. However, due to expense and man hours required for mechanical separation, it is generally inefficient for cleaning large areas. On the other hand, chemical cleaning methods are generally hazardous, e.g., require working with highly caustic solutions at high temperatures, and often damage the substrate being cleaned.
In an attempt to overcome many of the problems associated with mechanical and chemical methods of paint removal, it has been a common practice to apply a primer release coating to the substrate prior to paint deposition. The primer release coating operates as an interface between the substrate and the paint and facilitates the removal of the paint therefrom. Thus, effective primer release coatings generally have high cohesive strengths, poor adhesion and are easily removed from the substrate.
Heretofore, several methods of paint removal employing such primer release coatings have been proposed. For example, due to their poor adhesion to many substrates, ethyl cellulose, cellulose acetate butyrate or a vinyl polymer such as polyvinyl butyral have been proposed as primer release coatings. See, for example, Paint Manufacture, Volume 40, No. 7, Y. M. Chandhok and S. N. Agarwal, "Strippable Coatings", pages 35-37. Unfortunately, these primer release coatings, and the paint deposited thereon, are necessarily removed from the substrate by mechanicalstripping. Thus, paint removal employing such primer release coatings is unsuited for removing paint from intricate structures such as floor grates and for cleaning large areas.
Alternatively, methods for removing paint employing water-soluble primer release coatings have been proposed. For example, U.S. Pat. No. 1,862,392 describes a method of paint removal wherein a primer release coating comprised primarily of pigment, sulphonated castor oil, glycerine, mineral oil, water and alcohol is employed. Similarly, other water-soluble materials such as an alkali metal hypophosphate have also been disclosed as primer release coatings. See U.S. Pat. No. 3,846,172. Unfortunately, removal of paint deposited on these coatings requires steam or hot water, e.g., 70.degree. to 95.degree. C. Moreover, the removal of these coatings proceeds slowly, making these methods impractical for cleaning large areas.
In view of the stated deficiencies of the known methods for removing paint from a substrate, it remains highly desirable to provide a method for effectively removing paint from a substrate using a water wash.